2017 Vol. 41, No. 12
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The production of the X(3872) as a hadronic molecule in hadron colliders is clarified. We show that the conclusion of Bignamini et al., Phys. Rev. Lett. 103 (2009) 162001, that the production of the X(3872) at high pT implies a non-molecular structure, does not hold. In particular, using the well understood properties of the deuteron wave function as an example, we identify the relevant scales in the production process.
We study the scattering of massless Dirac fermions by Schwarzschild and Reissner-Nordström black holes. This is done by applying partial wave analysis to the scattering modes obtained after solving the massless Dirac equation in the asymptotic regions of the two black hole geometries. We successfully obtain analytic phase shifts, with the help of which the scattering cross section is computed. The glory and spiral scattering phenomena are shown to be present, as in the case of massive fermion scattering by black holes.
We expect that BR(χc2(2P)→ gluongluon)≥ 2% if the Particle Data Group as well as the BaBar and Belle collaborations have correctly identified the state. In reality, this branching ratio corresponds to the one for χc2(2P) decaying into light hadrons. We also discuss the detection possibilities of these decays.
If the neutrino mass spectrum turns out to be m3 < m1 < m2, it may be relabeled as m'1 < m'2 < m'3 such that all the masses of fundamental fermions with the same electrical charges are in order. In this case the columns of the 3×3 lepton flavor mixing matrix U should be reordered accordingly, and the resulting pattern U' may involve one or two large mixing angles in the standard parametrization or its variations. Since the Majorana neutrino mass matrix remains unchanged in such a mass relabeling, a possible μ-τ reflection symmetry is respected in this connection and its breaking effects are model-independently constrained at the 3σ level by using current experimental data.
We examine in detail a recent work (D. Gülmez, U. G. Meißner and J. A. Oller, Eur. Phys. J. C, 77:460 (2017)), where improvements to make ρρ scattering relativistically covariant are made. The paper has the remarkable conclusion that the J=2 state disappears with a potential which is much more attractive than for J=0, where a bound state is found. We trace this abnormal conclusion to the fact that an "on-shell" factorization of the potential is done in a region where this potential is singular and develops a large discontinuous and unphysical imaginary part. A method is developed, evaluating the loops with full ρ propagators, and we show that they do not develop singularities and do not have an imaginary part below threshold. With this result for the loops we define an effective potential, which when used with the Bethe-Salpeter equation provides a state with J=2 around the energy of the f2(1270). In addition, the coupling of the state to ρρ is evaluated and we find that this coupling and the T matrix around the energy of the bound state are remarkably similar to those obtained with a drastic approximation used previously, in which the q2 terms of the propagators of the exchanged ρ mesons are dropped, once the cut-off in the ρρ loop function is tuned to reproduce the bound state at the same energy.
Within the dinuclear system (DNS) model, the multinucleon transfer reactions 129,136Xe + 248Cm, 112Sn + 238U, and 144Xe + 248Cm are investigated. The production cross sections of primary fragments are calculated with the DNS model. By using a statistical model, we investigate the influence of charged particle evaporation channels on production cross sections of exotic nuclei. It is found that for excited neutron-deficient nuclei the charged particle evaporation competes with neutron emission and plays an important role in the cooling process. The production cross sections of several exotic actinide nuclei are predicted in the reactions 112Sn + 238U and 136,144Xe + 248Cm. Considering the beam intensities, the collisions of 136,144Xe projectiles with a 248Cm target for producing neutron-rich nuclei with Z=92-96 are investigated.
Continuum Discretized Coupled-Channel (CDCC) model calculations of total, complete and incomplete fusion cross sections for reactions of the weakly bound 6Li with 144,154Sm targets at energies around the Coulomb barrier are presented. In the cluster structure frame of 6Li→α+d, short-range absorption potentials are considered for the interactions between the ground state of the projectile 6Li and α-d fragments with the target. In order to separately calculate complete and incomplete fusion and to reduce double-counting, the corresponding absorption potentials are chosen to be of different range. Couplings to low-lying excited states 2+,3- of 144Sm and 2+,4+ of 154Sm are included. So, the effect on total fusion from the excited states of the target is investigated. Similarly, the effect on fusion due to couplings to resonance breakup states of 6Li, namely, l=2, Jπ=3+,2+,1+ is also calculated. The latter effect is determined by using two approaches, (a) by considering only resonance state couplings and (b) by omitting these states from the full discretized energy space. Among other things, it is found that both resonance and non-resonance continuum breakup couplings produce fusion suppression at all the energies considered.
We investigate the spectrum of the low-lying 1/2- hidden strange pentaquark states, employing the constituent quark model, and looking at two ways within that model of mediating the hyperfine interaction between quarks-Goldstone boson exchange and one gluon exchange. Numerical results show that the lowest 1/2- hidden strange pentaquark state in the Goldstone boson exchange model lies at~1570 MeV, so this pentaquark configuration may form a notable component in S11(1535) if the Goldstone boson exchange model is applied. This is consistent with the prediction that S11(1535) couples very strongly to strangeness channels.
The experimental rotational spectra of superdeformed (SD) bands of 130La, 131Ce(1,2), 132Ce(1,2,3) and 133Ce(1,2,3) in the A~130 mass region are systematically analyzed with the four parameter formula, power index formula, nuclear softness formula, and VMI model. It is observed that out of all the formulae, the four parameter formula suits best for the study of the 130La, 131Ce(1,2), 132Ce(2,3) and 133Ce(1,2,3) SD bands. The four parameter formula works efficiently in determining the band head spin of the 130La, 131Ce(1,2) 132Ce(2,3) and 133Ce(1,2,3) SD bands. Good agreement is seen between the calculated and observed transition energies whenever the accurate spin is assigned. In 132Ce(1), the power index formula is found to work better than the other three formulae. The dynamic moment of inertia is also calculated for all the formulae and its variation with the rotational frequency is investigated.
Pion properties at finite temperature, finite isospin and baryon chemical potentials are investigated within the SU(2) NJL model. In the mean field approximation for quarks and random phase approximation fpr mesons, we calculate the pion mass, the decay constant and the phase diagram with different quark masses for the m u quark and m d quark, related to QCD corrections, for the first time. Our results show an asymmetry between μI<0 and μI>0 in the phase diagram, and different values for the charged pion mass (or decay constant) and neutral pion mass (or decay constant) at finite temperature and finite isospin chemical potential. This is caused by the effect of isospin symmetry breaking, which is from different quark masses.
Quadrupole and octupole deformation energy surfaces, low-energy excitation spectra, and electric transition rates in eight neutron-rich isotopic chains-Ra, Th, U, Pu, Cm, Cf, Fm, and No-are systematically analyzed using a quadrupole-octupole collective Hamiltonian model, with parameters determined by constrained reflection-asymmetric and axially-symmetric relativistic mean-field calculations based on the PC-PK1 energy density functional. The theoretical results of low-lying negative-parity bands, odd-even staggering, average octupole deformations <β3>, and B(E3; 31-→ 01+) show evidence of a shape transition from nearly spherical to stable octupole-deformed, and finally octupole-soft equilibrium shapes in the neutron-rich actinides. A microscopic mechanism for the onset of stable octupole deformation is also discussed in terms of the evolution of single-nucleon orbitals with deformation.
We study ΛK+ pair production in the interaction of protons of 2.83 GeV kinetic energy with C, Cu, Ag, and Au target nuclei in the framework of the nuclear spectral function approach for incoherent primary proton-nucleon and secondary pion-nucleon production processes, and processes associated with the creation of intermediate Σ0K+ pairs. The approach accounts for the initial proton and final Λ hyperon absorption, final K+ meson distortion in nuclei, target nucleon binding, and Fermi motion, as well as nuclear mean-field potential effects on these processes. We calculate the Λ momentum dependence of the absolute ΛK+ yield from the target nuclei considered, in the kinematical conditions of the ANKE experiment, performed at COSY, within the different scenarios for the Λ-nucleus effective scalar potential. We show that the above observable is appreciably sensitive to this potential in the low-momentum region. Therefore, direct comparison of the results of our calculations with the data from the ANKE-at-COSY experiment can help to determine the above potential at finite momenta. We also demonstrate that the two-step pion-nucleon production channels dominate in the low-momentum ΛK+ production in the chosen kinematics and, therefore, they have to be taken into account in the analysis of these data.
The α decay half-life of the unknown nucleus 297Og is predicted within the two-potential approach, and α preformation probabilities of 64 odd-A nuclei in the region of proton numbers 82 < Z < 126 and neutron numbers 152 < N < 184, from 251Cf to 295Og, are extracted. In addition, based on the latest experimental data, a new set of parameters for α preformation probabilities considering the shell effect and proton-neutron interaction are obtained. The predicted α decay half-life of 297Og is 0.16 ms within a factor of 4.97. The predicted spin and parity of the ground states for 269Sg, 285Fl and 293Lv are 3/2+, 3/2+ and 5/2+, respectively.
Extremely powerful astrophysical electromagnetic (EM) systems could be possible sources of high-frequency gravitational waves (HFGWs). Here, based on properties of magnetars and gamma-ray bursts (GRBs), we address "Gamma-HFGWs" (with very high-frequency around 1020 Hz) caused by ultra-strong EM radiation (in the radiation-dominated phase of GRB fireballs) interacting with super-high magnetar surface magnetic fields (~1011 T). By certain parameters of distance and power, the Gamma-HFGWs would have far field energy density Ωgw around 10-6 and they would cause perturbed signal EM waves of ~10-20 W/m2 in a proposed HFGW detection system based on the EM response to GWs. Specially, Gamma-HFGWs would possess distinctive envelopes with characteristic shapes depending on the particular structures of surface magnetic fields of magnetars, which could be exclusive features helpful to distinguish them from background noise. Results obtained suggest that magnetars could be involved in possible astrophysical EM sources of GWs in the very high-frequency band, and Gamma-HFGWs could be potential targets for observations in the future.
Based on the relativistic theory of superstrong magnetic fields (SMF), by using three models those of Lai (LD), Fushiki (FGP), and our own (LJ), we investigate the influence of SMFs due to strong electron screening (SES) on the nuclear reaction 23Mg (p,γ) 24Al in magnetars. In a relatively low density environment (e.g., ρ7<0.01) and 1 < B12 < 102, our screening rates are in good agreement with those of LD and FGP. However, in relatively high magnetic fields (e.g., B12>102), our reaction rates can be 1.58 times and about three orders of magnitude larger than those of FGP and LD, respectively (B12, ρ7 are in units of 1012G, 107 g cm-3). The significant increase of strong screening rate can imply that more 23Mg will escape from the Ne-Na cycle due to SES in a SMF. As a consequence, the next reaction, 24Al (β+, ν) 24Mg, will produce more 24Mg to participate in the Mg-Al cycle. Thus, it may lead to synthesis of a large amount of A > 20 nuclides in magnetars.
We analyze the four common types of finite-time singularity using a generic framework of the phase portrait geometric approach. This technique requires the Friedmann system to be written as a one-dimensional autonomous system. We employ a scale factor that has been used widely in the literature to realize the four finite-time singularity types, then we give a detailed discussion for each case showing possible novel models. Moreover, we show how different singularity types can play essential roles in different cosmological scenarios. Among several modified gravity theories, we show that the f(T) cosmology is compatible with the phase portrait analysis, since the field equations include Hubble derivatives only up to first order. Therefore, we reconstruct the f(T) theory which generates these phase portraits. We also perform a complementary analysis using the effective equation of state. Furthermore, we investigate the role of the torsion fluid in realizing the cosmic singularities.
Pulsars are rapidly spinning, strongly magnetized neutron stars. Their electromagnetic dipole radiation is usually assumed to be at the expense of the rotational energy. In this work, we consider a new channel through which rotational energy could be radiated away directly via neutrinos. With this new energy conversion channel, we can improve the chemical heating mechanism that originates in the deviation from β equilibrium due to spin-down compression. The improved chemical and thermal evolution equations with different magnetic field strengths are solved numerically. The results show that the new energy conversion channel could raise the surface temperature of neutron stars, especially for weak field stars at later stages of their evolution. Moreover, our results indicate that the new energy conversion channel induced by the non-equilibrium reaction processes should be taken into account in the study of thermal evolution.
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